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# Trigonometry question watch

1. Hi can someone please the question in the image I have attached. I only need to know the one circled and need it to 1 d.p. Help is appreciated!
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2. Hi can someone please the question in the image I have attached. I only need to know the one circled and need it to 1 d.p. Help is appreciated!
The crucial part is that the line is the bisector of angle BAC. This means it divides it into two equal parts, i.e. two parts of 20 degrees each. Using this information you can get the length of CB and DB, which can be used to find the length of CD...
3. anyone?
4. you should activate your windows xp

bisector - what does that mean?
5. If the line AD is the bisector of the angle BAC (this means it splits it into two equal segments), and angle DAC is 20 degrees, how big are the angles BAC and BAD? Knowing this, how could you work out the length of line BC? And how would you use this to work out x? Note that BC = x + DC...
6. its easy... tan 40 = CB/AB
tan 40 * AB = CB

CD= 1/2 * CB
7. (Original post by Rick-Raith)
its easy... tan 40 = CB/AB
tan 40 * AB = CB

CD= 1/2 * CB
I'm afraid you're wrong here.
8. (Original post by TheNack)
I'm afraid you're wrong here.
actually i am not... it is a right angled triangle (cosine, tan, sine can be used)
we are given one angle and told it is a bi sectioning (therefore the whole angle there is 40)
and due to tan... opposite / adjacent = tan [angle]
angle = 40
tan 40 = CB/26

CD= CB/2 (due to the bi-sectioning)

therefore tan 40 * 26 = CB

...

its basic trig, i really don't see how it is difficult
9. Yes, you have that bit right, but it is wrong to say that CB = 2*CD i.e. the bit I highlighted.
10. (Original post by TheNack)
Yes, you have that bit right, but it is wrong to say that CB = 2*CD i.e. the bit I highlighted.
can you explain? cause if this is so, then i am probably going to do terribly in my maths exam tomorrow (which doesn't actually happen) but just curious to understand your logic behind this
11. (tan 40 - tan 20)26 = x

viola
12. bisector
bicycle
bisexual
binomial
bilateral
biannual

What do they all have in common?
13. (Original post by TheNack)
Yes, you have that bit right, but it is wrong to say that CB = 2*CD i.e. the bit I highlighted.
ok i worked out how it is wrong... but the answer is still pretty simple...

from working out CB... you work out DB using the same principles and do
CB-DB=CD

sorry hey...

(proved myself wrong by using a 3,4,5 triangle and working out the angle then doing the same steps)
14. (Original post by Rick-Raith)
can you explain? cause if this is so, then i am probably going to do terribly in my maths exam tomorrow (which doesn't actually happen) but just curious to understand your logic behind this
26*tan(40)=CB

26*tan(20)=BD

If CB=2*BD, then tan(40)=2*tan(20), but as this isn't the case (work it out on your calculator) then CB cannot be equal to 2*BD.

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